1. Field of the Invention
The field of the invention relates to a motor and to a disk drive unit having such a motor.
2. Summary of the Prior Art
A disk drive for a magnetic or optical disk normally has, a spindle motor for rotating the disk support, a head for reading or writing information to or from the disk, and an actuator for moving the head relative to the rotation axis. By suitable combination of disk rotation and head movement, data on the disk can be scanned by the head. Normally, both the spindle motor and the head actuator are located on the same side of the disk.
Improvements in disk technology have permitted the size of disks to be reduced, but this has resulted in the diameter of the disk becoming comparable with the diameter of the spindle motor. If the spindle motor is located directly below the disk support, the obstruction presented by the spindle motor limits the amount of the disk that can be scanned by the head. If, on the other hand, the spindle motor is spaced from the disk support by a distance sufficient to permit the head to pass therebetween, the size of the disk drive perpendicular to the plane of the disk is increased. A similar disadvantage occurs if the diameter of the spindle motor is reduced, since then its length perpendicular to the disk needs to be increased in order to provide a suitable drive force.
It has also been proposed to make use of an induction motor with an open section, and the actuator for head movement then being aligned with that open section to permit the head to be moved within the open section, and so closer to the axis of rotation than would otherwise be possible.